Right, Facebook is not a court, police force, or anything else with legal jurisdiction. Assuming the problem is that Trump is issuing an orders to the military that are illegal, that's not a problem that Facebook can police. The President can likely find another means of issuing illegal military orders that bypasses Facebook.
Reddit and numerous other sites have no issue displaying nipples (and more) with nothing more than a “are you over 18” modal. If any of those sites start running afoul of law enforcement you might have a point.